The present invention relates in general to rotatable heat exchangers, sometimes known as heat recovery wheels, and, in particular, it relates to a novel mounting structure for such heat recovery wheels.
In gas turbines, furnaces, and other combustion chambers it is desirable to preheat incoming combustion gases with heat extracted from exhaust gases, thereby increasing combustion efficiency. Rotary heat exchangers or heat recovery wheels are particularly desirable for this purpose. Heat recovery wheels are generally mounted for rotation about a central axis. The wheel first rotates through the exhaust gas stream. The wheel contains apertures extending therethrough in an axial direction and as gases flow through the apertures, heat is extracted from the exhaust gas stream and absorbed by the wheel. As the wheel further rotates through the incoming gas stream, heat is given up by the wheel, thus preheating the incoming gas.
While heat recovery wheels may be made from metal, ceramic materials are preferred because ceramic materials have a low coefficient of expansion and a high resistance to oxidation and to corrosion. However, even though ceramics are chosen for the body of such wheels, metals are still employed for the hub. Since the coefficient of thermal expansion of the metal hub differs from the coefficient of expansion of the ceramic, it is generally necessary to securely mount the wheel to its hub while permitting differential thermal expansion of the hub in the radial direction with respect to the wheel. U.S. Pat. No. 3,774,675--Yoshiro discloses such a mounting arrangement. In the Yoshiro patent, pads are provided which are radially expandable within the bore of the ceramic heat recovery wheel. A plurality of spring means are provided which bias the pads radially outwardly. One problem associated with the aforementioned Yoshiro patent is that the pads shown therein create undesirable tensile forces upon the ceramic structure. It is well known that ceramics are able to withstand large compressive forces, however, they are unable to withstand tensile forces of the same magnitudes. Accordingly, it would be desirable to provide an improved mounting structure, over that disclosed by Yoshiro, which minimizes the tensile forces exerted upon a ceramic disc.